Low currency redundancy anti-fuse method and apparatus

ABSTRACT

A programmable circuit includes a first node and provides a programmed signal based on the state of the first node. A first anti-fuse has a programmed state and an unprogrammed state and couples the first node to a first power supply when in the programmed state and decouples the first node from the first power supply when in the unprogrammed state. A second anti-fuse has a programmed state and an unprogrammed state and couples the first node to a second power supply when in the programmed state and decouples the first node from the second power supply when in the unprogrammed state. The state of the programmed signal can be used to replace a primary circuit element of an integrated circuit with a redundant circuit element.

This application is a division of U.S. patent application Ser. No.08/724,851, filed Oct. 3, 1996.

FIELD OF THE INVENTION

The present invention relates generally to integrated circuits, and moreparticularly to fuse-controlled programmable circuits used to replaceprimary circuit elements with redundant circuit elements in integratedcircuits such as memory integrated circuits.

BACKGROUND OF THE INVENTION

Technological advances have permitted semiconductor integrated circuitsto comprise significantly more circuit elements in a given silicon areaReducing and eliminating defects in the circuit elements has, however,become increasingly more difficult with the increased number of circuitelements. To achieve higher population capacities, circuit designersstrive to reduce the size of the individual circuit elements to maximizeavailable die real estate. The reduced size makes these circuit elementsincreasingly susceptible to defects caused by material impurities duringfabrication. Nevertheless, the defects are identifiable upon completionof the integrated circuit fabrication by testing procedures, either atthe semiconductor chip level or after complete packaging. Scrapping ordiscarding defective integrated circuits when defects are identified iseconomically undesirable, particularly if only a small number of circuitelements are actually defective.

Relying on zero defects in the fabrication of integrated circuits is anunrealistic option. Therefore, redundant circuit elements are providedon integrated circuits to reduce the number of scrapped integratedcircuits. If a primary circuit element is determined to be defective, aredundant circuit element is substituted for the defective primarycircuit element Substantial reductions in scrap are achieved by usingredundant circuit elements without substantially increasing the cost ofthe integrated circuit

One type of integrated circuit device which uses redundant circuitelements is integrated memory circuits, such as dynamic random accessmemories (DRAMs), static random access memories (SRAMs), video randomaccess memories (VRAMs), and erasable programmable read only memories(EPROMs). Typical integrated memory circuits comprise millions ofequivalent memory cells arranged in arrays of addressable rows andcolumns. The rows and columns of memory cells are the primary circuitelements of the integrated memory circuit. By providing redundantcircuit elements, either as rows or columns, defective primary rows,columns, or individual bits can be replaced.

Because the individual primary circuit elements (rows or columns) of anintegrated memory circuit are separately addressable, replacing adefective circuit element typically entails blowing fuses or anti-fusesin fuse-controlled programmable circuits to "program" a redundantcircuit element to respond to the address of the defective primarycircuit element This process is very effective for permanently replacingdefective primary circuit elements.

In the case of DRAMs, for example, a particular memory cell is selectedby first providing a unique row address of the row in which theparticular memory cell is located and subsequently providing a uniquecolumn address of the column in which the particular memory cell islocated. Redundancy circuitry must recognize the address of theeffective primary circuit element and reroute all signals to theredundant circuit element when the address to the defective primarycircuit element is presented by the user. Therefore, a number of fusesor anti-fuses are associated with each redundant circuit element. Thepossible combinations of blown and unblown fuses corresponding to eachredundant circuit element represent unique addresses of all primarycircuit elements for which a corresponding redundant circuit element maybe substituted

During testing of the DRAM, or other integrated circuit, at the factory,any defective primary circuit elements are identified. A suitableredundant circuit element is selected, and the corresponding fuses oranti-fuses are blown in a predetermined order to represent the addressof the defective primary circuit element to be replaced. When using theDRAM, each address provided to the DRAM must be compared to thecorresponding fuses or anti-fuses to determine if a redundant match ispresent. Whenever the redundant match is detected, the primary circuitelement is suppressed and the redundant circuit element is activated toperform the required function.

As mentioned above, fuses or anti-fuses can be used in thefuse-controlled programmable circuits. In a DRAM, an anti-fuse istypically a nitrite capacitor which is essentially a normal memory arraycell used as a blowable capacitor. Thus, no extra process steps arerequired in the fabrication of a DRAM to produce an anti-fuse. Unlikethe fuse which is open after being blown, the anti-fuse is typically aone-time blowable or programmable element which remains shorted when thecircuit is powered down and re-powered up. One problem with an anti-fusecontrolled programmable circuit is that once the fuse has been blown (orshorted), current is drawn through the anti-fuse. As more programmableanti-fuse circuits are disposed in an integrated circuit, and programmedby blowing the anti-fuses, the cumulative current drawn through theanti-fuses can be significant and can possibly affect the operation ofthe integrated circuit.

Conventional anti-fuse controlled programmable circuits use long-Lp-channel transistors to pull up anti-fuses. The long-L p-channeltransistor effectively decreases the amount of current drawn through ablown (shorted) anti-fuse to ground. Nevertheless, the resulting standbyand operating current due to a resistor short between the power rail andground when anti-fuses have been programmed is still somewhatsignificant. Moreover, the long-L p-channel transistor of existinganti-fuse structures occupies significant real estate in the integratedcircuit. Thus, although the length of the pull-up "long-L" p-channeltransistor can be increased to decrease the current drawn between thepower rail and ground, the increased length results in even more areabeing occupied by the long-L p-channel transistors of the anti-fusecontrolled programmable circuits.

Therefore, there is a need in the art for, an anti-fuse controlledprogrammable circuit which substantially eliminates or significantlyreduces the resulting standby current from blown or programmedanti-fuses. Moreover, there is a need for an improved anti-fusecontrolled programmable circuit which occupies less area in theintegrated circuit.

SUMMARY OF THE INVENTION

The present invention provides a programmable circuit coupled to a firstpower supply and a second power supply for providing a programmed signalin an integrated circuit. The programmable circuit includes a firstnode. The state of the programmed signal is based on the state of thefirst node. A first anti-fuse has a programmed state and an unprogrammedstate and couples the first node to the first power supply when in theprogrammed state and decouples the first node from the first powersupply when in the unprogrammed state. A second anti-fuse has aprogrammed state and an unprogrammed state and couples the-first node tothe second power supply when in the programmed state and decouples thefirst node from the second power supply when in the unprogrammed state.

In one embodiment of the programmable circuit according to the presentinvention, the first anti-fuse and the second anti-fuse each include afirst terminal and a second terminal. The first terminals of the firstand second anti-fuses are coupled to the first node. A first programmingbus carries a sufficient voltage to short the first anti-fuse. A firstswitch is coupled to the second terminal of the first anti-fuse andcouples the second terminal of the first anti-fuse to the first powersupply during normal operation of the integrated circuit and couples thesecond terminal of the first anti-fuse to the first programing busduring a first programming operation of the integrated circuit forprogramming the first anti-fuse. A second programming bus carries asufficient voltage to short the second anti-fuse. A second switch iscoupled to the second terminal of the second anti-fuse and couples thesecond terminal of the second anti-fuse to the second power supplyduring normal operation of the integrated circuit and couples the secondterminal of the second anti-fuse to the second programing bus during asecond programming operation of the integrated circuit for programmingthe second anti-fuse.

In one embodiment of the present invention the second power supplycomprises a ground node and the programmable circuit includes a switchcoupled between the ground node and the first node. The switch isresponsive to at least one programming control signal received by theprogrammable circuit. The switch is closed to couple the first node tothe ground node during a programming operation of the integrated circuitand open during normal operations of the integrated circuit. The switchpreferably is implemented in a transistor.

In one embodiment of the present invention the second power supplycomprises a ground node and the programmable circuit includes a switchcoupled between the ground node and the first node. The switch isresponsive to an enable signal received by the programming circuit. Theswitch is closed to couple the first node to the ground node based onthe enable signal being in a first state. The switch is open based onthe enable signal being in a second state. The switch preferably isimplemented in a transistor.

In one application of the present invention the integrated circuitincludes primary circuit elements, such as memory cells of a memoryintegrated circuit The integrated circuit also includes at least oneredundant circuit element. A selected one of the primary circuitelements is replaceable by the at least one redundant circuit elementbased on the state of the programmed signal.

The programmable circuit according to the present invention includes twoanti-fuses, with only one of the two anti-fuses being programmed,instead of a single anti-fuse to produce two states on the programmedsignal. In the programmable circuit of the present invention, noresistive short exists between the power supply and ground after theprogramming the programmable circuit, because only one of the twoanti-fuses is programmed which leaves the unprogrammed anti-fuse open.This substantially decreases or substantially eliminates current drawnthrough a blown or shorted anti-fuse to ground. This also eliminates theneed for long-L p-channel transistors to pull up the anti-fuses, whichprovides a substantial area saving in the integrated circuit employingnumerous programmable circuits according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are illustrations of a suitable configuration of a 64megabit DRAM having redundancy circuitry according to the presentinvention.

FIG. 2 is a block diagram of match anti-fuse bank circuit according tothe present invention, which is employed in the DRAM partiallyillustrated in FIGS. 1A-1C.

FIG. 3 is a more detailed block diagram of the match anti-fuse bank ofcircuit of FIG. 2.

FIG. 4 is a schematic diagram of a single anti-fuse controlledprogrammable circuit employed in the match anti-fuse bank of FIG. 2 forgenerating an enable bit.

FIG. 5 is a schematic diagram of a dual anti-fuse controlledprogrammable circuit employed in the match anti-fuse bank of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized and structural or logical changes may bemade without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

The following described embodiments of the present invention aredescribed as applied to a dynamic random access memory (DRAM). Thepresent invention is not limited to DRAMs, as the present invention isequally applied to other memory devices such as static random accessmemories (SRAMs), video random access memories (VRAMs), and erasableprogrammable read only memories (EPROMs). In fact, the present inventioncan be applied to any electronic integrated circuit having primary andredundant circuitry comprising separately addressable circuit elements.

Example DRAM Configuration

Addressable memory cells of a 64 megabit DRAM according to the presentinvention are illustrated generally at 20 in FIG. 1A. The 64 megabitDRAM according to the present invention is similar in many respects toconventional DRAMs, such as those commercially available from MicronTechnology, Inc. of Boise, Id. For clarity, only a portion of the wellknown circuitry of the DRAM is described herein, while the new circuitryof the DRAM of the present invention is described in detail herein. Asillustrated in FIG. 1A, the 64 megabit DRAM includes eight sections 22.As illustrated in FIG. 1B, each section 22 includes eight sub-sectionsor arrays 24. As illustrated in FIG. 1C, each array 24 includes onemegabit of memory cells arranged in 512 addressable primary rows orcircuit elements 26 and 2048 addressable primary columns or circuitelements 28.

In addition, in the embodiment of the 64 megabit DRAM according to thepresent invention illustrated in FIGS. 1A-1C, each array 24 includesfour addressable redundant rows or circuit elements 30 and fouraddressable redundant columns or circuit elements 32. Four redundantrows and four redundant columns are shown in FIG. 1C for illustrativepurposes only, and the exact number of redundant circuit elementsincluded in a DRAM or other integrated circuit according to the presentinvention is determined based on known design criteria.

Each primary row 26 is uniquely addressable. Thus, any one of theprimary rows 26 in the DRAM can be addressed using twelve address lines(i.e., nine address lines corresponding to the 512 primary rows 26 andthree address lines corresponding to the eight sections 22). If testingprocedures indicate that a primary row is defective, a redundant row 30is "programmed" to replace the defective primary row 26. This isaccomplished by programming a redundant row 30 to respond to the addresscorresponding to the defective primary row 26.

Each primary column 28 is also uniquely addressable. Thus, anyone of theprimary columns 28 in the DRAM can be addressed using fourteen addresslines (i.e., eleven address lines corresponding to the 2048 primarycolumns 28 and three address lines corresponding to the eight arrays24). If testing procedures indicate that a primary column is defective,a redundant column 32 is "programmed" to replace the defective primarycolumn 28. This is accomplished by programming a redundant column 32 torespond to the address corresponding to the defective primary column 28.

Match Anti-Fuse Bank Circuit

Referring to FIG. 2, each of the four redundant rows 30 and each of thefour redundant columns 32 of each array 24 includes a correspondingmulti-bit address/anti-fuse comparison circuit module or match anti-fusebank circuit 40 according to the present invention. Each match anti-fusebank circuit 40 is capable of receiving a multi-bit address signal,indicated at 42, in the form of a pre-decoded signal or a non-predecodedsignal depending on the embodiment of the match anti-fuse bank. Theaddress signal 42 is used to address the primary rows 26 at one time andthe primary columns at a subsequent time based on the state of selectedcommand input signals to the DRAM. Each match anti-fuse bank circuit 40is selectively programmable to respond to a specific value of theaddress signal 42. Each match anti-fuse bank circuit 40 evaluates theaddress signal 42 and activates a match signal, indicated at 44, if therow address value of address signal 42 corresponds to the address of adefective primary row 26 which the match anti-fuse bank circuit isprogrammed to replace. Similarly, each match anti-fuse bank circuit 40activates the match signal 44 if the column address value of addresssignal 42 corresponds to the address of a defective primary column 28which the match anti-fuse bank circuit is programmed to replace.

The match signal 44, when activated by the corresponding match anti-fusebank circuit 40, causes the associated redundant row 30 or theassociated redundant column 32 to be accessed. The activated matchsignal 44 also disables the associated defective primary row 26 or theassociated primary column 28 such that the associated defective primaryrow or column cannot respond to the address signal 42.

A more detailed schematic diagram of match anti-fuse bank circuit 40 isillustrated in FIG. 3. As illustrated in FIG. 3, match anti-fuse bank 40comprises `i` dual anti-fuse controlled programmable circuits 50 tocorrespond to address bits A0* through Ai* received from address signal42. Match anti-fuse bank 40 also comprises a single anti-fuse controlledprogrammable circuit 52 to receive a high-order address bit A_(i+1) *from address signal 42.

A fuse program (FP*) signal derived from the row address strobe (RAS)signal to the DRAM is provided on a line 64 to single anti-fusecontrolled programmable circuit 52. A fuse bank select (FBSEL*) signalis provided on a line 66 to single anti-fuse controlled programmablecircuit 52 and to all dual anti-fuse controlled programmable circuits 50on a line 66. FBSEL* is typically a high-order address bit which is lowwhen the particular fuse bank is selected for programming. A test modesignal (PRG*) which indicates that anti-fuses can be programmed whenlow, is provided on a line 68 to single anti-fuse controlledprogrammable circuit 52 and to all dual anti-fuse controlledprogrammable circuits 50.

Single anti-fuse controlled programmable circuit 52 provides a F* signalon a line 54. The F* signal on line 54 is provided to one input of a twoinput NOR gate 56. An inverter 57 inverts the PRG* signal to produce aPRG signal on a line 69. The PRG signal on line 69 is provided to theother input of NOR gate 56. NOR gate 56 provides an EN* (enable) signalon a line 58 to all of the dual anti-fuse controlled programmablecircuits 50. When the EN* signal is low, the dual anti-fuse controlledprogrammable circuits 50 are enabled for programming. Each of the dualanti-fuse controlled programmable circuits 50 provide a corresponding F*signal on a corresponding line 60 which are all provided to a comparelogic circuit 62 along with the F* signal on line 54 from singleanti-fuse controlled programmable circuit 52. In addition, the EN*signal on line 58 and address inputs A<0:(i+1)> on line 42 are alsoprovided to compare logic circuit 62. Compare logic circuit 62 providesthe match signal indicated at 44, which is activated if every singleaddress input A0-Ai+1 matches the corresponding state of thecorresponding anti-fuses in the anti-fuse controlled programmablecircuits 50 and 52 as indicated by the F* signals.

A program/ground CGND bus 70 is provided to single anti-fuse controlledprogrammable circuit 52 and to all dual anti-fuse controlled circuits50. In addition, a program/power CVCC bus 72 is provided to all dualanti-fuse controlled programmable circuits 50. The operation of the CGNDbus 70 and the CVCC bus 72 are described below in reference to FIGS. 4and 5.

Single Anti-Fuse Controlled Programable Circuit for Enable Bit

Single anti-fuse controlled programmable circuit 52 is illustrated inmore detail in schematic diagram form in FIG. 4. The layout of singleanti-fuse controlled programmable circuit 52, as illustrated in FIG. 4,is similar to conventional anti-fuse controlled programmable circuitsfor the individual address bits of prior art match anti-fuse bankcircuits. Single anti-fuse controlled programmable circuit 52, however,is used to generate. the EN* signal on line 58 in the match anti-fusebank circuit 40 according to the present invention.

As illustrated in FIG. 4, a three input NOR gate 80 receives the PRG*signal on line 68, the FBSEL* signal on line 66, and the Ai+1* signal online 42 (i+1) and activates an output line 82 when all three inputsignals are a low-logic level. The output of NOR gate 80 on line 82 isprovided to the gate of an n-channel transistor 84. The source ofn-channel transistor 84 is coupled to a ground node. The drain ofn-channel transistor 84 is coupled to a node 86. With the PRG*, FBSEL*and the Am* signals all low, line 82 becomes high to turn transistor 84on. With transistor 84 on, node 86 is effectively coupled to the groundnode. An

An anti-fuse 88 has one of its terminals coupled to node 86 and itsother terminal coupled to a switch 90. Switch 90 switches between aground node and the CGND bus 70. During programming, the switch 90switches to the CGND bus 70 and during normal operations, switch 90switches to the ground node. In this way, during programming oneterminal of anti-fuse 88 is coupled to a ground level at node 86 and theother terminal is coupled to the CGND bus 70. In programming anti-fuse88, a high voltage such as 10 volts, or the voltage needed to exceed thebreakdown voltage of anti-fuse 88 to permanently short anti-fuse 88, isprovided on the CGND bus 70.

Node 86 is also coupled to the input of an inverter 92 which suppliesthe F* signal on line 54 from single anti-fuse controlled programmablecircuit 52. The F* signal is coupled to the gate of a p-channeltransistor 94. The source of p-channel transistor 94 is coupled to theVcc power supply. The FP* signal on line 64 is provided to the gate of ap-channel transistor 96. The source of p-channel transistor 96 iscoupled to the Vcc power supply. The drains of p-channel transistors 94and 96 are coupled together and coupled to the source of a long-Lp-channel pull-up transistor 98. The gate of long-L p-channel pull-uptransistor 98 is coupled to ground. The drain of long-L p-channelpull-up transistor 98 is coupled to node 86.

In operation, when anti-fuse 88 is not programmed (open), node 86 ispulled toward VCC to provide a low or zero output on the F* line 54.Thus, the EN* signal, which is an inverted version of the F* signal online 54 when the PRG signal on line 69 is low, is at a high level whenthe "enable" anti-fuse 88 is not blown or programmed. When anti-fuse 88is programmed (shorted), node 86 is pulled to the ground level, whichwhen inverted by inverter 92, produces a high or one output on the F*line 54. Thus, the EN* signal, which is an inverted version of the F*signal on line 54 when the PRG signal on line 69 is low, is at a lowlevel to enable programming of the dual anti-fuse controlledprogrammable circuits 50 after "enable" anti-fuse 88 is blown.

Dual Anti-Fuse Controlled Programmable Circuit

Dual anti-fuse controlled programmable circuit 50 is illustrated in moredetail in schematic diagram form in FIG. 5. As illustrated in FIG. 5, aNOR gate 100 receives the PRG* signal on line 68, the FBSEL* signal online 66, and an individual address bit indicated by Am* on the 42 (m)line. NOR gate 100 activates an output line 102 when all three inputsare low. The output of NOR gate 100 on line 102 is coupled to the gateof an n-channel transistor 104. The source of n-channel transistor 104is coupled to ground. The drain of n-channel transistor 104 is coupledto a node 106. With the PRG*, FBSEL* and the Am* signals all low, line102 becomes high to turn transistor 104 on. With transistor 104 on, node106 is effectively coupled to the ground node.

An anti-fuse 108 has one of its terminals coupled to node 106 and itsother terminal coupled to a switch 110. Switch 110 switches between aground node and the CGND bus 70. During programming, the switch 110switches to the CGND bus 70 and during normal operations, switch 110switches to the ground node. In this way, during programming oneterminal of anti-fuse 108 is coupled to a ground level at node 106 andthe other terminal is coupled to the CGND bus 70. In programminganti-fuse 108, a high voltage such as 10 volts, or the voltage needed toexceed the breakdown voltage of anti-fuse 108 to permanently shortanti-fuse 108, is provided on the CGND bus 70.

An anti-fuse 112 has one of its terminals coupled to node 106 and itsother terminal coupled to a switch 114. Switch 114 switches between aground node and the CVCC bus 72. During programming, the switch 114switches to the CVCC bus 72 and during normal operations, switch 114switches to the Vcc power supply or a DVC2 power supply. In this way,during programming one terminal of anti-fuse 112 is coupled to a groundlevel at node 106 and the other terminal is coupled to the CVCC bus 72.In programming anti-fuse 112, a high voltage such as 10 volts, or thevoltage needed to exceed the breakdown voltage of anti-fuse 112 topermanently short anti-fuse 112, is provided on the CVCC bus 72.

As indicated above, in one embodiment of the present invention, oneterminal of anti-fuse 112 is coupled to DVC2, having a Vcc/2 level,instead of the full Vcc power supply. In this embodiment, the Vcc/2potential across anti-fuse 112 reduces or substantially eliminatespotential reliability problems that can result from having a full Vccpotential across anti-fuse 112. However, with anti-fuse 112 tied toDVC2, or other lower voltage than Vcc, the output inverter 116 needs tobe skewed to operate at a reduced input swing voltage.

Node 106 is also coupled to an inverter 116. Inverter 116 inverts thestate on node 106 and provides the F* signal on the line 160 for theindividual address bit Am*.

The EN* signal, as stated above, is high before the enable fuse 88 ofsingle anti-fuse controlled programmable circuit 52 is programmed. TheEN* signal being high prevents inverter 116 from having a floating inputat node 106. The EN* signal is provided from line 58 to the gate of ann-channel transistor 118. N-channel transistor 118 has its sourcecoupled to the ground node and its drain coupled to node 106. Thus, whenthe EN* signal is high, n-channel transistor 118 is turned on to couplenode 106 to ground to produce a low input into inverter 116 and a highoutput on F* line 60. When the EN* signal is brought low with theprogramming of anti-fuse 88 of single anti-fuse controlled programmablecircuit 52, or with the PRG* signal going low to produce a high PRGsignal on line 69, n-channel transistor 118 is turned off to enable thecircuit to operate appropriately as described below.

In operation, when anti-fuse 108 is not programmed (left open) andanti-fuse 112 is programmed (shorted), node 106 is brought to Vcc orDVC2 (a high-logic level). The high-logic level is inverted by inverter116 to provide a low or zero output on the F* signal on line 60. Whenanti-fuse 108 is programmed (shorted) and anti-fuse 112 is notprogrammed (left open), node 106 is tied to the ground node (a low-logiclevel). Inverter 116 inverts the low-logic level to provide a high orone output on the F* signal on line 60.

By programming one of either anti-fuse 108 or 112, the user of the DRAM,or other integrated circuit according to the present invention, canselect the desired state of the output F* signal of anti-fuse controlledprogrammable circuit 50. As described above, dual anti-fuse controlledprogrammable circuit 50 is employed in match fuse bank 40 illustrated inFIGS. 2 and 3 for programming to respond to specific values of theaddress signal 42 for replacing primary circuit elements, such as row orcolumns of a DRAM, with redundant circuit elements. Dual anti-fusecontrolled programmable circuit 50 is, however, alternatively embodiedin a variety of circuit applications where a programming feature isrequired. For example, multiple dual anti-fuse controlled programmablecircuits 50 are employed to generate a fuse identification (ID) for anintegrated circuit The fuse ID is a pattern of binary digits whichuniquely identify the integrated circuit chip and can be decoded afterthe chip is packaged or integrated onto a circuit board.

Dual anti-fuse controlled programmable circuit 50 is alternativelyembodied in another form of the present invention to select a mode ofoperation in the integrated circuit. For example, the amount of refreshavailable in a memory integrated circuit can be controlled with multipledual anti-fuse controlled programmable circuits 50, such as by selectingbetween 4K rows or 8K rows in a 64 Meg DRAM. Another mode of operationapplication is to utilize dual anti-fuse programmable circuit 50 forslowing down or speeding up the integrated circuit. In another mode ofoperation application dual anti-fuse controlled programmable circuits 50is employed to select either a fast page mode for a memory integratedcircuit or an extended data out (EDO) mode for the memory integratedcircuit.

In any of its implementations, the dual anti-fuse structure of dualanti-fuse controlled programmable circuit 50 of the present inventioneliminates the need for a long-L p-channel pull-up transistor, such aslong-L p-channel pull-up transistor 98 of single anti-fuse programmablecircuit 52. In addition, the standby current resulting in conventionalanti-fuse controlled programmable circuits, such as single anti-fusecontrolled programmable circuit 52, resulting when the single anti-fuseis programmed or shorted to cause a resistive connection between the Vccpower supply and ground, is substantially eliminated with dual anti-fusecontrolled programmable circuit 50. The standby current no longer existsbecause one of anti-fuses 108 or 112 remains open so that there issubstantially no connection created between the Vcc power supply andground.

The dual anti-fuse controlled programmable circuit 50 of the presentinvention occupies significantly less space in an integrated circuitthan the conventional type single anti-fuse controlled programmablecircuit 52. Assuming one n-channel transistor occupies approximately thesame space as one p-channel transistor, there is the equivalent of oneless normal p-channel transistor in the dual anti-fuse controlledprogrammable circuit 50, because n-channel transistor 118 replaces thetwo p-channel transistors 96 and 94. Most significantly, the long-Lp-channel pull-up transistor 98 is completely eliminated in the dualanti-fuse controlled programmable circuit 50. Although the dualanti-fuse controlled programmable circuit 50 adds one anti-fuse over thesingle anti-fuse controlled programmable circuit 52, the additionalspace occupied by the additional anti-fuse is much less than the spaceneeded for one normal p-channel transistor and one long-L p-channeltransistor. Thus, the net effect is a significant savings in die areawhen the dual anti-fuse controlled circuits of the present invention areemployed in an integrated circuit, such as in match anti-fuse bankcircuit 40 of FIG. 3.

Conclusion

The match anti-fuse bank circuit according to the present inventionutilizing the dual anti-fuse controlled programmable circuit 50according to the present invention operates with only one of the dualanti-fuses being programmed. Therefore, no resistive short between theVcc power supply and ground is established, which substantiallydecreases or eliminates current drawn through a blown or shortedanti-fuse to ground. This also eliminates the need for long-L p-channeltransistors to pull up the anti-fuses, which provides a substantial areasaving in the integrated circuit employing dual anti-fuse programmablecircuits according to the present invention.

Although specific embodiments have been illustrated and described hereinfor purposes of description of the preferred embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent implementations calculated to achieve thesame purposes may be substituted for the specific embodiments shown anddescribed without departing from the scope of the present invention.Those with skill in the mechanical, electro-mechanical, electrical, andcomputer arts will readily appreciate that the present invention may beimplemented in a very wide variety of embodiments. This application isintended to cover any adaptations or variations of the preferredembodiments discussed herein. Therefore, it is manifestly intended thatthis invention be limited only by the claims and the equivalentsthereof.

What is claimed is:
 1. A programmable circuit coupled to a first powersupply and a second power supply for providing a programmed signal in anintegrated circuit comprising:a first node, wherein the state of theprogrammed signal is based on the state of the first node; a firstanti-fuse including a first terminal coupled to the first node and asecond terminal coupled to the first power supply; a second anti-fuseincluding a first terminal coupled to the first node and a secondterminal coupled to the first power supply; a first programming buscarrying a sufficient voltage to short the first anti-fuse; a firstswitch coupled to the second terminal of the first anti-fuse forcoupling the second terminal of the first anti-fuse to the first powersupply during normal operation of the integrated circuit and couplingthe second terminal of the first anti-fuse to the first programing busduring a first programming operation of the integrated circuit forprogramming the first anti-fuse to couple the first node to the firstpower supply; a second programming bus carrying a sufficient voltage toshort the second anti-fuse; and a second switch coupled to the secondterminal of the second anti-fuse for coupling the second terminal of thesecond anti-fuse to the second power supply during normal operation ofthe integrated circuit and coupling the second terminal of the secondanti-fuse to the second programing bus during a second programmingoperation of the integrated circuit for programming the second anti-fuseto couple the first node to the second power supply.
 2. The programmablecircuit of claim 1 further comprising:a switch coupled between thesecond power supply and the first node and responsive to at least oneprogramming control signal received by the programmable circuit, whereinthe switch is closed to couple the first node to the second power supplyduring a programming operation of the integrated circuit and open duringnormal operations of the integrated circuit.
 3. The programmable circuitof claim 2 wherein the switch comprises a transistor.
 4. Theprogrammable circuit of claim 1 further comprising:a switch coupledbetween the second power supply and the first node and responsive to anenable signal received by the programming circuit, wherein the switch isclosed to couple the first node to the second power supply based on theenable signal being in a first state, and wherein the switch is openbased on the enable signal being in a second state.
 5. The programmablecircuit of claim 4 wherein the switch comprises a transistor.
 6. Theprogrammable circuit of claim 1 wherein the second power supplycomprises a ground node.